This invention relates to a bogie for supporting a vehicle upon the rails of a railroad track. Further, this invention relates to a rail grinder using the bogie.
Various wheel arrangements have been used for rail vehicles over the years. Vehicles which are sufficiently short may use a two axle four wheel arrangement. However, that design has a wheel base equal to the distance between the two axles. When moving around a tight curve, the long wheel base may hold the wheels at an angle which is not tangent to the curvature of the rail. Depending upon the tightness of the curve and the length of the wheel base, this may cause the wheel flanges to bind against the rail, leading to derailment.
Transit cars and other relatively large rail vehicles which are used on tight curves avoid the problem of out-of-tangent wheels by use of a double bogie eight wheel arrangement. Each bogie has four wheels and pivots (steers) about a central vertical axis. The bogie wheel base is usually short enough (four to five feet) to prevent the out of tangent situation described above. Each bogie has a center pivot corresponding to its central vertical axis such that the bogie may follow the rail curvature.
The prior art bogie system is shown in a schematic top view of FIG. 1 as having four wheels 10 which pivot as a unit about the central pivot corresponding to a vertical axis. In certain applications, such as various rail maintenance vehicles, use of bogies having short wheel bases would be desirable. However, a bogie with a short wheel base is relatively unstable and may oscillate about the center pivot. The instability is caused by the minimal leverage of the wheel flange forces (see FIG. 1) about the center pivot. The tangential forces created by propulsion and rolling resistance try to turn the bogie. This is resisted by the wheel flange forces. If the bogie wheel base is relatively long, the required flange forces are small. However, when the wheel base is relatively small, the flange forces increase. The increase causes the wheel flange to start walking up the rail head. This allows the bogie to pivot. Once the flange force overcomes the tangential forces, the bogie has pivoted and is now out of balance and the oscillation begins. Therefore, center pivot bogies have generally not been suitable for applications where one wishes to have a relatively short wheel base.
Among various prior rail maintenance machines is the RAIL GRINDER of the Shoenhair et al U.S. Pat. No. 4,779,384, issued Oct. 25, 1988, assigned to the assignee of the present invention, and hereby incorporated by reference. That patent disclosed a rail grinder vehicle having numerous grinders mounted thereto and using a two axle four wheel arrangement with a 10 foot wheel base. The grinders have grind stones used to grind out various deformities which occur after use of a rail. The grinders are mounted upon a so-called K frame, which in turn is pivotably connected to a vehicle main frame. The rail grinder of that patent uses a four wheel two axle arrangement of the type discussed above.
The rail grinder of the Shoenhair design has been quite useful. However, the grinder may not be able to grind unusually tight curves. The schematic top view of FIG. 2 shows eight grinding stones 12 (only some labeled) on a vehicle (vehicle not shown for simplicity). As the vehicle goes around a curve in the rails, the grinding stones have a chordal offset which is too large to allow the grinding heads to operate properly.
The problem of grinding stones becoming offset from the rails limits the application of some grinding machines to exclude rail sections having relatively tight curves. At least some designs have used vehicles having separate rail grinding carriages attached underneath the vehicle. The carriages have their own wheels separate from the vehicle wheels and they use the wheels of the carriage to allow the grinding heads to track rail curvature and minimize chordal offset. Although these arrangements may work, they are subject to several disadvantages. They require a relatively larger number of wheels than would otherwise be the case. They complicate the structure of the machine.